Profit-seeking developers are to be warned by Ed Miliband that they could be stripped of land if they fail to build homes on it.
So-called "use it or lose it" powers are among policies being considered by Labour to ease housing shortages and boost the construction industry.
Recent research found there were 400,000 homes that have not been built despite councils giving planning permission. That is roughly the equivalent of Birmingham, where the Labour leader will set out the proposals to the party's National Policy Forum on Saturday.
The Opposition say the figure gives the lie to Conservative claims that town halls were causing delays by dragging their feet on approving homes. They also said developers' profits had soared by 72% to almost £1 billion last year despite building fewer homes,
Mr Miliband will accuse firms of "sitting on land, waiting for it to accumulate in value" - frustrating families' chances of affording a home. Homelessness charity Shelter said this week that young people face having to save for up to 30 years for a first-time deposit.
"There is nothing more important in family life than having a home," Mr Miliband is due to tell the weekend event. "Nobody should be in any doubt about this Labour Party's determination to rebuild this country, get our construction industry working again and give families a decent chance of owning a decent home for their children, just like their parents did before them. But to do that we have to be willing to confront some of the obstacles to house building. Across our country, there are firms sitting on land, waiting for it to accumulate in value and not building on it. Land-owners with planning permission, who simply will not build. We have to change that."
Figures compiled by the Local Government Association found that at the end of 2011, there were 399,816 unbuilt homes with planning permission. In more than half of unfinished cases, no work had been done at all and the average time taken to complete a project had increased by a quarter to 25 months in just four years.
Labour said that, although councils could already forcibly buy land in extreme cases where there was an "overwhelming public interest", the party was looking at reducing the threshold for deploying the option.
Planning minister Nick Boles said: "Yet again Ed Miliband is too weak to offer a coherent policy. Most normal planning permissions already expire after a three-year period and councils don't have to renew them. Labour clearly learnt nothing from its failures in government as 400,000 homes represents less than two years' worth of the number of new homes that we need to build. And confiscating any land from development will not help build a single house.
"We're already incentivising developers to build 170,000 affordable new homes for hard-working people by getting mortgage lending flowing again; using our Getting Britain Building scheme; unlocking development on stalled sites and renegotiating planning permission for sites that weren't previously commercially viable to build on - which Labour opposed. Ed Miliband's only real plan is the same old Labour answer that got us into this mess in the first place - more spending, more borrowing and more debt. And hard-working people would pay the price."